Ultimate Limit State Risk Assessment of Penta Pod Suction Bucket Support Structures for Offshore Wind Turbine due to Scour

The scour risk assessment was conducted for ultimate limit state of newly developed penta pod suction bucket support structures for a 5.5 MW offshore wind turbine. The hazard was found by using an empirical formula for scour depth suitable for considering marine environmental conditions such as significant wave height, significant wave period, and current velocity. The scour fragility curve was calculated by using allowable bearing capacity criteria of suction foundation. The scour risk was assessed by combining the scour hazard and the scour fragility.

Interpretation of uplift pipeline-soil interaction behaviour using acoustic emission measurements

The objective of this study was to develop quantitative acoustic emission (AE) interpretation for uplift pipeline-soil interaction behaviour, enabling early warning of serviceability and ultimate limit state failures in the field. A series of large-scale uplift experiments was performed on a steel pipe in sand with different burial depths (i.e., stress levels), and varying rates of deformation were imposed. A suite of AE parameters was compared with the pipe force and displacement behaviour. Image-based deformation measurements were used to monitor the soil displacement field. AE generation was proportional to the imposed stress level and pipe displacement rate and related to the evolution of the pipe/soil failure mechanism. Relationships have been quantified between AE generation and stress level (R2 values of 0.99), and between AE generation rate and pipe velocity (R2 values ranging from 0.95 to 0.98), enabling interpretation of accelerating deformation behaviour that accompanies progressive ground failure processes. An example interpretation framework demonstrates how AE parameters can be used to identify the mobilisation of peak uplift resistance and quantify accelerating deformation behaviour during post-peak softening.

COMPARATIVE ANALYSIS OF COMPOSITE TIMBER-CONCRETE CEILING SYSTEMS

This paper compares two concepts of composite timber concrete ceilings and their uncoupled alternatives based on a parametric study by comparing the final deflections of individual variants and at the same time considering according to the ultimate limit state. It includes a comparison of coupled and uncoupled variants while maintaining the same boundary conditions as the load, the thickness of the ceiling structure and the load width. By considering other factors, we can achieve more optimal variant, thanks to more accurate consideration of the required boundary conditions such as the complexity of installation or fire resistance. The purpose of this paper is to simplify the optimal selection of the ceiling structure based on the suitability of the supporting structure.

A RATIONALIZED SEISMIC DESIGN METHOD FOR BUILDINGS IN EARTHQUAKE-PRONE DEVELOPING COUNTRIES

In general, the US codes such as the UBC-97 and ASCE-7 are widely used in developing countries including Myanmar, Syria, Philippines and so on. When the current seismic design guideline based on the UBC-97 and ACI 318-99 in Myanmar is assessed, several problems can be found in the following items: firstly, the fundamental period is not checked in modeling; secondly, reduction factor R is introduced a priori for the base shear estimation. And finally, a limit state assessment is done only for Design Basic Earthquake (DBE) but not for other design earthquakes. As a result, adequate yield strength is not checked for Maximum Operational Earthquake (MOE). Then there is no way to assess the seismic safety of the ultimate limit state for Maximum Considered Earthquake (MCE). In order to solve these problems, a rationalized seismic design method for earthquake prone developing countries is proposed. A new seismic design method is developed for MOE and MCE with adequate yield acceleration and typical period of the building estimated by using pushover analysis. A simplified procedure to estimate the inelastic response for a given design spectrum is also proposed. Finally, this design procedure can provide a rational method to assess the seismic safety for the ultimate limit of the building.

Calibration of resistance factors for bearing resistance design of shallow foundations under seismic and wind loading

Although the geotechnical resistance 19 factors at ultimate limit state used for dynamic loading conditions should be different from those for static loading conditions, most current structural and geotechnical design codes do not specifically provide dynamic resistance factors. In this paper, the ultimate limit state reliability analysis of individual shallow foundations for drained and undrained soil conditions under seismic (pseudo-dynamic) and wind loads using the Random Finite Element Method is carried out using the provisions of the National Building Code of Canada. The geotechnical resistance factors required to achieve target maximum lifetime failure probabilities are estimated for a few major Canadian cities. The results indicate that the failure probability for drained soil conditions is slightly greater than that for undrained soil conditions. In addition, the results suggest that the dynamic resistance factors for foundation bearing capacity design at ULS are lower than those for static foundation design specified by the code. The current analysis can be used to guide the calibration of these geotechnical resistance factors.

A Proposal to Improve the Effectiveness of the Deflection Control Method Provided by Eurocodes for Concrete, Timber, and Composite Slabs

Limited deflection of structural members represents an important requirement to guarantee proper functionality and appearance of building and infrastructures. According to Eurocodes, this requirement is ensured by limiting the maximum deflection of horizontal structural members to a fraction of their span. However, each Eurocode provides different maximum deflection limits, which are independent of the type of superstructures considered. Thus, the respect of these limits may not always guarantee the integrity of certain superstructures. In this paper, the reliability of the Eurocode deflection control methods, in guaranteeing the integrity of the superstructures, is assessed and discussed. First, different types of horizontal member, namely rib and clay (hollow) pot, composite steel–concrete, and timber beam slabs are designed to respect the deflection limit enforced by the Eurocodes. Then, the maximum curvature developed by these members is compared with the ultimate (limit) curvatures of various superstructures (e.g., ceramic and stone tile floorings). The results obtained show that the approach adopted by Eurocode 2 may provide non-conservative results, but also that the rules proposed by Eurocodes 4 and 5, albeit more reliable, do not always guarantee the integrity of the superstructure. Based on these results, an alternative method, based on the curvature control, is proposed and its advantages and limitations critically discussed. This method appears simpler and more reliable than the method currently adopted by the Eurocodes.

METHODS FOR CALCULATING RECTANGULAR SECTION BEAMS MADE OF WOOD AND CONCRETE

The research aimed to study methods for calculating wood-concrete beams of rectangular cross-section when testing building structures according to the ultimate limit state. The article focuses on the comparison of theoretical methods for calculating structures and considers several methods of fastening the samples of a typical wood-concrete beam. There were obtained experimental data of the ultimate limit state for each sample and carried out a comparative analysis of the most advantageous scheme of fastening the sample parts. The scientific novelty is in the development of an algorithm for calculating composite wood-concrete beams of rectangular cross-sections. As a result, numerical comparison of the values for calculating a typical wood-concrete beam using two of the methods under consideration was given, experimental studies were carried out, as well as a comparative analysis of the obtained theoretical and experimental results.

Causes of Failures in Circular Concrete Silo Walls, Particularly Under Environmental Influences

The paper reports the results of a case study for achieving longer service life and increasing the environmental sustainability of concrete silos. Damage mechanisms in concrete silo walls, and respectively in cylindrical structures (e.g., chimneys, cooling towers, and tanks), are widely diverse. The common causes of failures include those due to poor design considerations, construction deficiencies, non-compliance with operational rules and regulations, lack of maintenance, and insufficient and/or corroded reinforcements, together with the environmental conditions affecting the walls. In addition to the ultimate limit state design, temperature-induced cracking may often be underestimated in the design of reinforced concrete silos, leading to premature deterioration and losses in serviceability. Cracks from environmental or service conditions facilitate the ingress of moisture and corrosive agents. Therefore, there is an increased interest in reducing the appearance of cracks and limiting their width. The aim of this paper is to highlight the synergistic effects in the design, construction, and operation of silo walls, particularly under varying environmental influences. The research undertaken indicates that systematic errors can be identified and corrected.